Assessment of Indoor Environmental Quality (IEQ) in university classrooms by periods of the day through discriminant analysis

Indoor Environmental Quality (IEQ) is fundamental in any environment, as it directly influences occupants' health, comfort, well-being, and productivity. In educational environments, inadequate conditions can impair cognitive performance and learning. This research analyzed IEQ in naturally ventilated university classrooms in Brazil, aiming to identify how environmental conditions vary throughout the day and to evaluate whether such variations form statistically distinguishable patterns. To perform this investigation, discriminant analysis was adopted to classify environmental conditions considering four periods of the day : (1) early morning (7:30-9:59 a.m.), (2) mid/late morning (10:00-11:59 a.m.), (3) early afternoon (12:00-02:59 p.m.), and (4) mid/late afternoon (03:00-05:59 p.m.). A total of 150 measurements were collected between March 2024 and June 2025, covering parameters such as operative temperature, relative humidity, illuminance, CO2 concentration, levels of volatile organic compounds (VOCs), and noise, obtained by the Aura IEQ Discoverer® equipment. The results indicated that operative temperature, relative humidity, and CO2 were the main factors distinguishing environmental conditions across periods. The discriminant model achieved an original classification accuracy of 32.7% and a cross-validated accuracy of 25.3%, indicating that, although measurable variations exist, environmental conditions were not strongly separable across the day. Operative temperature increased in the afternoon due to heat accumulation and solar gains, while relative humidity decreased; CO2 concentration remained relatively stable, suggesting consistent air exchange through natural ventilation. These findings highlight that, in naturally ventilated classrooms, IEQ variations are moderate and reflect relative environmental stability. Such insights can inform practical strategies for ventilation, lighting, and noise control in educational environments, supporting thermal comfort, energy efficiency, acoustic comfort, and improved air quality, while also emphasizing the importance of understanding temporal patterns in real-world IEQ assessments.